Role of quantum fluctuations at high energies

We investigate an influence of virtual particles on the classical motion of a system in Minkowski and Euclidean spaces. Our results indicate that fluctuations of fields different from the main field decelerate significantly its motion at high energies. The formalism described here is applicable to the majority of inflationary models. We show also that the quantum fluctuations suppress false vacuum decay in first-order phase transitions at high energies.